Heart failure (HF) is a condition characterized by reduced cardiac output that triggers neurohormonal activation. This compensatory mechanism functions acutely to increase cardiac output and restore left ventricular (LV) functional capacity such that patients remain asymptomatic. Over time, however, sustained activation of these neurohormonal systems triggers pathologic LV remodeling and end-organ damage that ultimately drives the progression of HF.
In many people, persistent hypertension is the predominant contributing factor for development of HF. Management of hypertension can slow or prevent the natural evolution of HF.
The human body maintains blood pressure through the use of a central control mechanism located in the brain with numerous peripheral blood pressure sensing components. These components are generally made of specialized cells embedded in the walls of blood vessels that create action potentials at an increased rate as the cell is stretched. These groups of cells are generally referred to as baroreceptors. The action potentials are propagated back to the central control center via neural pathways along afferent nerves. While there are many baroreceptor components located throughout the body, there are several that are particularly important. Possibly the most important baroreceptor region is located near the bifurcation of the common carotid artery into the internal and external carotid. In this area there is a small enlargement of the vessel tissues, referred to as the carotid bulb or carotid sinus. The carotid baroreceptors are generally found throughout this area. The carotid baroreceptors and related neural pathways form the primary pressure sensing component that provides signals to the brain for regulating cranial and systemic blood pressure.
Applicant's prior Application Publication No. U.S. 2007/0255379, which is incorporated herein by reference, discloses an intravascular neurostimulation device (such as a pulse generator) and associated methods for using the neurostimulation device to stimulate nervous system targets. As discussed in that application, targeting stimulation to baroreceptor afferents in HF patients can lead to decreases in sympathetic tone, peripheral vascular resistance, and afterload. Such stimulation can be used to control blood pressure as a treatment for hypertension or HF. Stimulation of the vagus nerve (e.g. vagal efferents) is known to cause a reduction in heart rate.
The present disclosure describes an implementation of Applicants' previously-disclosed intravascular systems and methods for use in stimulating nervous system targets such as the vagus nerve and/or its branches, the carotid artery, the carotid sinus nerve and/or its branches, baroreceptors, and/or for otherwise activating a baroreceptor response. Systems and methods of the type disclosed may be used for controlling heart rate and/or regulating blood pressure for treatment of hypertension, congestive heart failure or other conditions.
The internal jugular vein, vagus nerve, and common carotid artery (which includes the carotid sinus) are located within the carotid sheath, a fascial compartment within the neck. The carotid sheath provides relatively fixed geometric relationships between these structures while also giving some degree of insulation from surrounding tissue. According to one embodiment disclosed herein, a method is disclosed for transvascularly stimulating contents of the carotid sheath. The method includes advancing an energy delivery element, which may be an electrode, into an internal jugular vein, retaining the energy delivery element in a portion of the internal jugular vein contained within a carotid sheath, and energizing the energy delivery element to transvenously direct energy to target contents of the carotid sheath external to the internal jugular vein. The energy may be directed to a carotid artery within the carotid sinus sheath, and/or to a carotid sinus nerve or nerve branch within the carotid sinus sheath, to nerve branches emanating from carotid artery baroreceptors, and/or to a vagus nerve or nerve branch within the carotid sinus sheath.
In some of the disclosed embodiments, a second electrode or other second energy delivery element is introduced into a second internal jugular vein and retained in a portion of the second internal jugular vein contained within a second carotid sheath. The second energy delivery element is energized to direct energy to contents of the second carotid sheath external to the second internal jugular vein.
Shielding may be used to minimize collateral stimulation of unintended targets. In one embodiment, a shield is positioned at least partially surrounding the carotid sinus sheath. The shield blocks conduction of energy beyond the sheath during energization of the energy delivery element. In another embodiment, an insulative material is delivered into extravascular space adjacent to the internal jugular vein. The insulative material defines a channel within the extravascular space. Energizing the energy delivery implant causes energy to conduct along the channel to the target contents of the sheath.
In some embodiments, the system may include a plurality of electrodes disposed on the lead, the electrodes including a first array and a second array, wherein the first and second arrays are positioned such that when the first array is positioned in the internal jugular vein to direct stimulation energy transvascularly to a vagus nerve in the carotid sheath, the second array is positioned to direct stimulation energy transvascularly towards a carotid artery or carotid sinus nerve/nerve branch within the carotid sheath. In other embodiments, the same array of electrodes delivers stimulus to each of the target structures within the carotid sheath.
The baroreceptors in the aorta are the second best understood baroreceptors and are also a powerful localized blood pressure sensing component. The aortic baroreceptors are also responsible for providing signals to the brain for regulating systemic/peripheral blood pressure. Some of the embodiments disclosed herein are positioned to transvascularly deliver energy to these baroreceptors and/or associated nerve structures as an alternative means for neurohormonal control.